The present invention relates to light emitting diodes (LEDs) and, more particularly, to an electrode structure for such LEDs as III-V compounds inclusive of GaP, GaAs, GaAs, GaAs.sub.1-x P.sub.x, Ga.sub.1-x Al.sub.x As and the like.
The conventional III-V compound LED comprises an N-type layer and a P-type layer both of which are grown with liquid phase epitaxy on an N-type wafer. The wafer is made with liquid encapsulated Czochralski method. An alloy such as Au-Be or Au-Zn is deposited upon the P-type layer as an ohmic contact electrode. Another alloy such as Au-Si or Au-Ge is deposited upon the N-type layer as the ohmic contact electrode. The P-type layer electrode is wire bonded with a gold wiring member to a conductive member by applying pressure and heat thereto.
The surface condition of the P-type layer electrode is determinative of whether the wire bonding with the gold wiring provides good adhesion. The metal of Zn or Be added to Au prevents the gold wiring from being tightly bonded to the electrode surface, thereby preventing good wire-bonding. Ga may possibly diffuse from the semiconductor substrate into the electrode due to the heat application procedure, preventing the gold wiring from being tightly bonded.
On the other hand, Al wirings adapted for Si devices can provide good wire bonding. However, the Al wirings can not provide good ohmic contact to III-V compounds, in particular, low impurity concentration layers such as GaP and GaAs which are made with liquid phase epitaxy.
Therefore, an improved electrode structure for providing good wire bonding and good ohmic contact is desirable.